.\" Copyright (c) 1990 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" the Systems Programming Group of the University of Utah Computer
.\" Science Department.
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.\"	@(#)dcm.4	5.1 (Berkeley) 6/29/90
.\"
.TH DCM 4 "June 29, 1990"
.UC 7
.SH NAME
dcm \- HP 98642A communications multiplexer
.SH SYNOPSIS
.B "device		dcm0	at scode? flags 0xe"
.SH DESCRIPTION
The 98642A is a four port EIA RS-232C (CCITT V.28) communications
multiplexer. The 98642A has three direct-connect ports and one port with
full modem control.
.PP
Each line attached to the 98642A behaves as described in
.IR tty (4).
Input and output for each line may set to one of following baud rates;
50, 75, 110, 134.5, 150, 300, 600, 1200, 1800, 2400, 4800,
9600, 19200, 38400. See 
.IR tty (4)
for the encoding.
.PP
Flags is usually specified as 0xe since 3 of the 4 ports (1-3) do not support
modem control and should be treated as hard-wired with carrier always present.
If port 0 does not have the need for modem control then flags can be specified
as 0xf.
.PP
Each port on the 98642A has a 128 byte input silo and a 16 byte output silo.
Interrupts happen on a per character basis unless the interrupt
rate for the card reaches 70 interrupts per second at which time the
driver changes to a 16.7ms (60 interrupts per second) polling scheme until 
the interrupt rate drops.
.SH FILES
/dev/tty0[0-9a-f]
.SH "SEE ALSO"
tty(4)
.SH DIAGNOSTICS
\fBdcm%d port%d: silo overflow\fR Input Silo has overflowed and incoming data
has been lost.
.PP
\fBdcm%d port%d: uart overflow\fR The 3 character buffer in the uart has
overflowed.
.SH BUGS
Total throughput per card, all ports together, is limited to 76800 bits per
second continuous input rate.